The present invention relates to disposable coasters usable underneath liquid containers, such as drinking glasses, beer cans, soft drink cans, pitchers, beer mugs, goblets, coffee cups, tea cups, etc. Such coasters serve a useful purpses, especially when the associated container contains a cold liquid. The cold liquid within the container causes moisture in the surrounding atmosphere to condense on the container outer surface and run down that surface onto the coaster. The liquid (water) collects on the coaster instead of flowing onto a table surface or dripping onto a person's clothing or onto the floor.
It is believed that for a coaster to be as effective as possible it should be capable of being adhered to the bottom surface of the container so that it will perform its condensate-collection function continuously, both while the container is at rest on a table surface and also when the container is being held in the person's hand above the table surface. Also, the coaster should be formed at least partially of a liquid-absorbing material so that liquid migrating onto the coaster surface will not be thrown or dislodged from the coaster when the container is moved around.
Coasters having some desired properties are already known. U.S. Pat. No. 2,004,166 to Low shows a coaster construction that includes an upper layer 8 formed of liquid-absorbent blotting paper, a lower layer 6 of liquid absorbent blotting paper, and an intervening glue film 7 between the two layers. Upper layer 8 will soak up condensate that forms on the outer surface of the associated container, and lower layer 6 will soak up water that may tend to form on the table surface. Especially in the case of containers containing cold liquids, the lower face of the coaster may be relatively cold, such that atmospheric moisture can condense at the table-coaster interfaces. Absorbent layer 6 of the coaster will tend to absorb such condensed moisture.
The coaster shown in Low U.S. Pat. No. 2,004,166 is not designed to adhere itself to the bottom surface of the associated liquid container. Thus, a person using the coaster must make a conscious effort to return the container to a position on the coaster after each sip of liquid; otherwise, condensate on the container surface will be apt to be thrown onto the person's clothing or onto the table surface.
Some difficulty would be encountered if it were desired to redesign the Low coaster so that it can adhere to a bottom surface of a container. Blotting paper has a very low wet strength. Therefore, if a film of adhesive were to be provided on the upper face of layer 8 of the Low coaster the coaster would nevertheless probably, in many instances, tear apart and separate from the container, leaving a glue film on the container surface. Also, the presence of a glue film between the container and coaster surfaces would constitute a barrier to flow of condensate from the container onto the moisture-absorbing area of the coaster.
U.S. Pat. No. 2,014,268 to Tenney discloses a coaster that includes an upper layer of 4 of glazed paper, three intermediate layers 7 formed of felt, sponge or blotting paper, and a bottom layer 6 of glazed paper. The intermediate layers 7 are of progressively increasing diameter so that condensate can flow radially outwardly from non-absorbant layer 4 onto peripheral edge areas of layers 7 for absorption therein.
Tenney indicates that moisture on the upper surface of his layer 4 can serve to adhere the coaster to the container bottom surface. Such might be the case if the container has a flat bottom surface that provides substantial contact area in engagement with the coaster surface, as shown in FIG. 1 of the Tenney drawings. Sufficient adherence could often not be obtained when the container has a recessed or non-flat lower face, as is often in the case.
Layer 4 in the Tenney coaster is moisture-impervious, such that condensate must flow off layer 4 onto edge areas of layers 7 in order to be absorbed into the coaster. The layers 7 apparently must have a stepped configuration, as shown in FIG. 3 of the Tenney drawings. Consequently, the coaster is required to have a diameter that is considerable larger than the diameter of the associated container.
U.S. Pat. No. 2,131,878 to Lawrence shows a coaster that includes an annular pad 12 of blotting paper or some absorbent fibre or fabric. An adhesive fabric layer 22 is secured to the lower face of pad 12; two crossing slots 26 are formed in adhesive layer 22, such that the central portion of layer 22 can be manually pushed upwardly through the large opening in pad 12 into adherent contact with the lower face of a liquid container.
The central opening in pad 12 subtracts substantially from the volume of pad 12 that could otherwise serve for condensate absorption. The Lawrence arrangement suffers also in that in many cases, a person might be unaware of the exact "push up" procedure required to adhere the coaster onto the container; additionally, it might prove inconvenient for the person to exert a push-up force on adhesive layer 12 after the container has been filled with liquid, because the filled container would be apt to spill liquid during manipulation of the container in one hand and the coaster in the other hand.
Another patent disclosing an adhesively-coated coaster is U.S. Pat. No. 2,163,309 issued to McConnell. The McConnell patent discloses a coaster formed out of several layers of soft paper napkin material 10. Slits 15 and 16 are formed in the coaster to permit the central area of the coaster to be pushed upwardly against the bottom surface of a liquid container, as shown in FIG. 3 of the McConnell drawings. A pressure sensitive adhesive 14 is disposed on the central area of the coaster to achieve adherence between the coaster and the container. The McConnell coaster design appears to be similar to the design shown in Lawrence U.S. Pat. No. 2,131,878, at least from a functional or operational standpoint.
The coaster of the present invention differs from the coaster of the above-referenced patents. My proposed coaster comprises an upper pad formed at least partly of moisture-absorbent material. The upper face of the pad has a large number of small adhesive patches extending in an annular ring pattern concentric with the pad central axis. The individual adhesive patches may be of any configuration and are spaced apart so that when the coaster is secured to the lower face of a liquid container, condensate will readily flow from the container surface into the pad via the adhesive-free areas of the pad upper face. Preferably, the adhesive patches are large in number and are such that a large number of potential liquid paths are provided through the intervening adhesive-free areas. The entire volume of the pad is available for liquid-absorbing purposes.
My proposed coaster includes a second lower pad formed of a thermally insulating material--e.g., a closed cell plastic foam material. This second pad may be bonded to the lower face of the upper pad by a liquid-impervious bonding agent applied as a continuous film across the interface between the two pads. The bonding agent acts as a barrier against downflow of liquid from the upper pad to the lower pad, whereby the lower pad remains in an essentially dry condition wherein it provides a relatively good insulating action.
This second pad is especially useful when the coaster is used with containers containing cold liquids. The pad insulates the subjacent table surface for the cold container temperature, and thus inhibits the formation of atmospheric condensate on the table surface. If the container contains hot liquid, the lower pad will insulate the liquid from the table surface and thus prevent surface damage due to excessive heat. The lower pad is mot useful when the container contains cold liquids because the pad prevents the formation of condensate on the table surface.
The second pad is not necessary for coasters used with hot dring containers, except as mentioned above, or in low-humidity climate areas where only minimal condensate is formed on cold drink containers. If a second lower pad is not used, only a waterproof film need be provided on the bottom of the first pad.
The coaster is designed so that a number of the coasters may be packaged together for sale as a unit package. The coasters may be stacked one atop another in a multi-layer three dimensional configuration. Alternately, the coasters may be adhered to a backing sheet. The backing sheet and attached coasters may be packaged in a flat configuration or rolled into a sprial package configuration suitable for being dispensed, one at a time, for a roll-type dispenser box.
When the coasters are packaged in a multi-layer three dimensional configuration, the adhesively-coated upper face of each coaster is facially engaged with the lower face on each superjacent coaster. The adhesives on the individual coasters thus hold the coasters together in the desired stack configuration. To enable individual coasters to be peeled off (separated) from the package when needed, the lower faces of the coasters will be coated with an adhesive release agent, such as a silicone coating or the like. The silicone fluid viscosity will be selected to achieve only a partial release of the adhesive action, such that individual coasters can be readily separated from the stack without causing premature separation of all coasters in the stack.